The invention relates to improvements in so-called mobile crushing plants which can be transported to and from locations where large quantities of building and/or other material must be crushed and, if necessary, classified according to size and/or other characteristics. Mobile crushing plants are manufactured by the assignee of the present application, and some of presently popular plants are known as Krokodil and Kaiman. Reference may be had to a publication entitled "Mobile Crushing and Screening Plant" which is distributed by the assignee.
It is already known to design the frame of a mobile crushing plant in such a way that one of its ends can be hitched to a towing vehicle, e.g., to a flat bed truck, and that the frame carries a comminuting machine as well as a feeding unit which serves to supply material to be crushed into the range of the comminuting machine. The frame and its wheels resemble a semitrailer. One end of the frame carries the comminuting machine and the other end of the frame serves as a means for supporting the inlet of the material feeding unit.
When a mobile crushing plant is in actual use, it is desirable to maintain the inlet of the material feeding unit as close to the ground as possible. Reference may be had to German Offenlegungsschrift No. 32 28 735 which discloses a mobile crushing plant with a frame serving to support a tiltable material feeding unit. When the frame is detached from a towing vehicle, the inlet of the feeding unit is tilted to a lower or lowermost level at a short distance above the ground. A drawback of the crushing plant which is disclosed in this printed publication is that the outlet in the lowermost portion of the comminuting machine is close to the respective portion of the frame and the frame is rather close to the ground so that it is not possible to move the receiving end of a standard take-off conveyor for comminuted material to a position for reception of material from the comminuting machine. The rear end portion of the frame cannot be raised or provided with a platform for the comminuting machine because this would move the machine to a level above that which is permissible for transport of the crushing plant on public roads. The just discussed publication proposes to provide a duct in the rear portion of the frame in order to establish a path for evacuation of comminuted material onto a conveyor in the frame. Such solutions cannot be resorted to in all kinds of crushing plants.
German Utility Model No. 85 34 877 proposes a different mobile crushing plant wherein the understructure of the endless conveyor of the material feeding unit constitutes the frame of a semitrailer and is located at a level below a crushing roll. The rear end portion of the frame is mounted on a set of wheels and supports the crushing roll. The rear end portion of the frame further carries lifting means serving to pivot the frame about a transversely extending horizontal axis so that the front end portion of the frame comes to rest on the ground. The comminuting machine is located above the axis so that its level does not change when the frame is tilted in order to lower its front end portion into contact with the ground.
German Pat. No. 31 10 444 discloses a mobile crushing plant wherein the entire frame can be lifted above the ground. Such lifting of the frame also entails a lifting of the wheels, and each portion of the frame is raised to the same extent. This solves the problem of raising the comminuting machine so as to provide room for a take-off conveyor beneath the outlet of the machine. However, the inlet of the material feeding unit is normally located at a level well above the ground. Therefore, it is necessary to provide discrete tilting means for the material feeding unit.